The scale on a map is 5cm : 8km. If two cities are 30cm apart on the map, what is the actual distance in km between the two cities?
Solution: The scale means that every 5cm on the map corresponds to an actual distance of 8km. A distance of 30cm on the map is the same as 6 $\cdot$ 5cm. The actual distance between the two cities is 6 $\cdot$ 8km, or 48km.